The present invention generally relates to multi-plate clutches and more particularly pertains to the extension of the service life of such devices as well as the reduction of the noise that is typically generated thereby.
Clutches are employed for interruptably coupling two rotating components to one another such as for example an engine to a transmission. A multi-plate clutch configuration offers significant advantages over a single-plate clutch configuration including the ability to accommodate a greater torque handling capability in an overall smaller package. As a consequence, such clutch configurations are found in a large variety of different applications including high-performance motorcycles and automobiles, trucks and heavy machinery. There are however some disadvantages associated with multi-plate clutch devices, including the propensity for the accelerated wear of its component parts and the noise that is caused by the interaction of the wearing parts.
In general terms, a multi-plate clutch employs a stack of drive plates and driven plates (friction plates) that are concentrically arranged in an alternating sequence along a common axis wherein one of the two sets of plates is keyed to an internally disposed shaft or carrier while the alternating set of plates is keyed to an externally disposed cylindrical shell or basket. The cylindrical shell is typically coupled to an engine while the internally disposed shaft is typically coupled to a transmission. Configurations in which the drive plates are steel and the driven plates are made of or coated with a friction material as well as configurations in which the drive plates are made of or coated with friction material and the driven plates are steel are both well known in the art. When the stack is compressed, the plate faces engage to become rotationally joined to one another and are thereby able to effectively transfer torque from the shell to the shaft or from the shaft to the shell. In the absence of a compressive force, the plates disengage and are free to spin relative to one another thereby interrupting the transfer of torque between the external shell and the internal shaft.
In keying the one set of plates to the externally disposed shell, it is essential that the plates remain readily axially shiftable relative thereto while being rotationally locked thereto. Each plate must be capable of axially shifting slightly as the stack of plates is compressed so as to take up the slack between the plates which had allowed the alternating plates to freely spin relative to one another. Conversely, when the compressive force is released, the plates must be able to readily shake free from the adjacent plates in order to rotationally decouple the shaft from the shell. This is typically accomplished by forming axially extending channels or slots in the externally disposed shell that are dimensioned to receive keys that are formed about the outer circumference of each plate. Each plate is thereby rotationally locked to the shell as one of the edges of each of the keys engages one or the other sidewall of the channel in which it resides while the keys are free to shift along the channels.
In order to ensure that the axial movement of the keys remains uninhibited under all operating conditions, the widths of the keys are typically selected to be slightly undersized relative to the widths of the channels. While this achieves the intended effect, it is the underlying cause of a number of shortcomings inherent in multi-plate clutches. The gap between the leading edge of each key and the sidewall of the channel allows the keys of each plate to slam into the respective channel sidewall or for the respective channel to slam into the keys with each change in the direction of torque transfer. This becomes especially problematic in automotive and motorcycle applications as such impacts will occur with every upshift and downshift, with every switch between accelerative loading and decelerative loading while in a gear and even when in neutral, as each firing pulse will cause the engine's output to undergo a brief acceleration and deceleration. These impacts not only generate noise and vibration, but cause the keys and/or channels to wear. Any such wear accelerates the rate of further wear along with a commensurate increase in noise and vibration as the impacts become harsher until the clutch becomes unserviceable.
A number of different approaches have heretofore been taken in effort to address the above-described problem inherent in multi-plate clutches. Reducing the tolerances between the keys and channels has generally been found to be of limited utility as the function of the clutch quickly becomes compromised. Close tolerances between the keys of each of the plates and the corresponding channels renders the keys prone to binding or jamming in the channels should the plates and/or associated keys become distorted, angled or otherwise misaligned. Such binding or jamming would prevent or delay the clutch from decoupling the driving and driven components when the compressive force is released thereby making it difficult to select neutral or shift gears. Conversely, binding or jamming could prevent or delay the clutch from effectively coupling the driving and driven components when the stack of plates is compressed. Most efforts have therefore focused on damping the impact of the leading edge of each key with the sidewall of the channel.
A well known approach entails the submersion of the entire clutch mechanism in a fluid wherein the fluid naturally fills any gaps and thereby serves to dampen the impact between a key and the sidewall. This is highly effective, greatly increases service life and reduces or even eliminates the noise. However, the oil used in so-called “wet” clutches introduces a significant amount of drag to thereby rob power and increase fuel consumption. Additionally, in four stroke motorcycle applications, such clutches tend to contaminate the engine oil.
An alternative approach entails the use of mechanical damping devices such as springs or O-rings that are fitted to or about the key/channel interface so as to buffer the impacts between the engaging surfaces. While such modifications have been found to be somewhat effective in reducing the impact loads and the associated noise and damage, the added components not only add complexity to the clutch mechanism but are more prone to failure. Damaged or broken metallic parts that come loose can cause further damage to the clutch and difficulty in its operation while broken O-rings can prevent plates from separating and shaking apart.
A multi-plate clutch configuration is needed that overcomes the shortcomings of presently known multi-plate configuration. It is most desirable to provide a multi-plate clutch that is not as prone to excessive wear rates, that does not generate noise during its operation and that does not suffer from the complexity of presently known efforts to address wear and noise. Additionally, it is most desirable to provide a means for modifying or retrofitting existing multi-plate clutches so as to extend service life.